The present invention relates to a sheet post-processing apparatus for feeding an image-formed sheet to a processing tray to perform post-processing, and then storing the sheet in a stack tray, and more particularly, improvements in a sheet transport mechanism for feeding and setting a sheet in a processing position on the processing tray with a correct posture.
Generally, this kind of post-processing apparatus is known as an apparatus which is connected to a sheet discharge outlet of an image formation apparatus, collates and collects image-formed sheets on a processing tray to perform post-processing such as binding processing, punching processing and stamping processing, and stores the processed sheets in a stack tray.
For example, Patent Document 1 discloses an apparatus which transports backward a sheet fed from an image formation apparatus to a processing tray disposed below a sheet discharge outlet, performs binding processing with a post-processing apparatus such as a stapler apparatus disposed in the tray, and stores the binding-processed sheets in a stack tray on the downstream side.
In the Document, a sheet discharge area is provided inside a housing of the image formation apparatus, and disclosed is the post-processing apparatus of inner finisher structure such that a post-processing unit is inserted in the sheet discharge area.
Further, Patent Document 2 discloses a mechanism which collects a subsequent sheet in a buffer path until the processing is finished during operation of the post-processing of a preceding sheet among sheets that are transported at high velocity from an image formation apparatus, aligns the sheet posture in the path, and then drops onto a downward processing tray to store.    [Patent Document 1] Japanese Patent Application Publication No. 2011-037591    [Patent Document 2] Japanese Patent Application Publication No. 2007-308215
Various kinds are known as the post-processing mechanism which transports a sheet fed from the image formation apparatus to the processing tray to perform post-processing, and then stores in the stack tray as described above. In the apparatus of Patent Document 1 as described previously, the processing tray is disposed with a height difference formed below a sheet discharge path, the transport direction is reversed from the sheet discharge path, and the sheet is carried in the processing tray from the rear end side. Then, the sheet that is carried onto the tray is positioned and aligned in the front and back in the sheet discharge direction and the left and right in the sheet-discharge orthogonal direction to reference positions, and therefore, it is difficult to find a correct processing position.
Then, the inventor of the present invention arrived at the idea of positioning the sheet front end in a regulation position (for example, sheet stopper) on the tray in feeding the sheet to the processing tray form the sheet discharge path, and then, causing the sheet rear end side to make a soft landing on the tray. At this point, the need arises for retracting a guide member that guides the sheet underside to carry the sheet front end in the tray and a sheet discharge roller brought into contact with the sheet underside to lateral positions away from the sheet, and dropping the sheet rear end side. However, it has a problem with space providing a retract mechanism for retracting a plurality of members inside limited space of the sheet discharge path and processing tray, and at the same, the problem arises that maintenance space when trouble occurs is not obtained.
It is an object of the present invention to provide a post-processing apparatus for preventing a sheet from becoming misaligned in dropping the rear end side of the sheet with the front end carried in the processing tray from the sheet discharge path to store on the tray, and enabling the mechanism to be simplified, compact and configured at low cost.